In practice, micromechanical components having a self-supporting diaphragm are used in the contexts of pressure sensors and thermal sensors such as mass flow sensors, thermal angle of inclination sensors, and thermal infrared detectors for example. In thermal sensors, the self-supporting diaphragm is used as a thermally insulated region having a low heat capacity.
German Patent Application No. 103 05 442, filed on Feb. 11, 2003, describes the manufacture of a micromechanical component having a self-supporting diaphragm, which includes multiple layers and is implemented in a pure front-side process. To this end, an appropriate layer system is first produced on the substrate of the component. To expose the diaphragm, orifices are then introduced into the layer system, which are oriented in essence perpendicularly to the layer planes and which completely penetrate the layer system, so that the orifices form an etching access path to the substrate. Starting at the front side, the substrate material in the region beneath the orifices is then removed in an isotropic etching step, it being possible to refer to the substrate down to the depth of the cavity thus created as a sacrificial layer.
The cavity formed beneath the diaphragm is in direct contact with the surroundings of the component via the etching access paths, so that dirt particles are able to penetrate the cavity unhindered and collect there. This generally has an adverse effect on the functionality of the component, and in extreme cases results in the total failure of the component.
German Patent Application No. 103 05 442 makes reference to the possibility of depositing a closing layer over the layer system after the diaphragm is exposed in order to close the etching access paths. In practice, however, this has proven to be problematic in several respects. Because the material of the closing layer grows on the diaphragm essentially in the vertical direction, the orifices in the diaphragm are closed only relatively slowly. This results in the formation of a relatively thick closing layer, which often adversely affects the mechanical as well as the thermal properties of the diaphragm. In addition, during production of the closing layer it is usually not possible to prevent the material of the closing layer from also depositing in the region of the cavity and in particular on the lower side of the diaphragm, which has an additional negative effect on the mechanical and thermal properties of the diaphragm. Finally, it should be noted that producing and processing a closing layer is associated with additional manufacturing expenditure.